The guys in YAGS and ZAGS have different preferences on anal sex and other forms of sex. This provides a bit of character background in a less fic-like and more expository form.
The fact that this exists on paper instead of just in my head is tmfoxed's fault.
Adam: Adam generally prefers to top. He will have moments when he'll actively want to bottom, usually after particularly emotional or sentimental moments (such as getting engaged, or seeing Chris again after a summer apart), and won't necessarily turn it down when requested, but disprefers it otherwise. He does not enjoy giving oral sex, but is onboard with receiving it. Adam generally disprefers casual sex, as he considers it to be a form of intimacy tied to an emotional connection.
Carlos: Carlos generally prefers to bottom, although he won't turn down requests to top, especially as part of group sex. He's open to and enjoys most other sexual acts, and has a bit of a masochistic streak, enjoying being tied, bound, hit, and generally used. He has a particular fetish for being fed his own cum. He will happily seek out casual sex with one or more others, although ultimately he does want one person he can exclusively commit emotionally (but not necessarily physically) to.
Chris: Chris is fairly down-the-middle and is happy to both top or bottom, although if given free choice, he'll usually choose to bottom. He is otherwise fairly vanilla, but derives much of his own sexual satisfaction out of satisfying his partner. He'd try new things when pushed, but prefers to stick to things he knows and is comfortable with. He only has sex within the bounds of a relationship, and would not be accepting of anything other than monogamy.
Dan: Dan exclusively tops, and will turn down any sexual act that involves anything in his anus, including fingers. He'll try anything at least once if it's not underage, or involving blood or feces. He did bottom once, early on in his sexual experimentation, but disliked it, and generally doesn't waste time with sexual acts he dislikes. He has a bit of a dom streak, liking to be in control of sex and his sexual partners, but ultimately does care for their comfort and pleasure, as well. Dan can emotionally commit to someone, but not physically, and monogamy is never on the table.
Elliot: Elliot generally prefers to top. However, Dan represented such a huge departure from the house (and he also does enjoy receiving) that he was drawn to him for his first sexual experimentation. Like Dan, Elliot is happy to experiment, but he'll ultimately settle on a somewhat smaller list of preferred acts, but can be pressed a bit beyond those, especially by a dedicated partner. He's not in any way a jealous person, and is generally open to any form of relationship. As such, he will either happily commit to monogamy or enjoy open relationships (even one-sided ones) with strict rules and guidelines, or make a real attempt at polyamory if asked.
Jake: Jake exclusively bottoms, but he's uncomfortable with the idea of sex in general. It takes him a while to feel comfortable and emotionally-close enough to someone that he's willing to make an attempt for them, but it's still something he enjoys doing for the sake of his partner(s) rather than for himself. As such, he'll initiate sex only when he feels like he wants to thank or congratulate his partner on some milestone, but will reciprocate if asked, and does derive happiness and pleasure from being able to satisfy his partners. Along those lines, he'll do most things if asked. (Jake honestly probably has a degree of asexuality in there.)
James: James is flexible and will happily top or bottom, although he'll usually default to topping if not requested otherwise. He treats sex as a means of communicating his love and affection in a way he can find difficult with words; as such, he generally has little interest in sex or masturbation outside the context of a relationship, but is almost insatiable within one. He is also fairly vanilla otherwise, enjoying oral sex, handjobs, and frotting, but it takes him a while to get over the unpleasantness of the logistics afterward. He requires commitment, an intense emotional connection, and (obviously) monogamy.
Malik: Malik doesn't do anal sex in any form, but is open to most other things and mostly aims to please. He isn't against the idea of casual sex, although he also doesn't want to spend the time seeking out someone (or someones). When in a relationship, he's happy to experiment, but mostly gets off on his partner's pleasure. He's not against the idea of open relationships, but generally disprefers them.
Nate: Nate generally prefers to top. However, he finds himself generally attracted to Dan's straighforward boorishness, finding it a welcome relief from both his gilded life growing up and what he considers the superficial world of business relationships, so he finds the tradeoff of only bottoming for him worthwhile. He's open to group sex, and although he'd prefer monogamy within a relationship, he also has a strong libido that must be met that takes priority over potential relationship strain. He's open to trying some more interesting sexual acts, but is otherwise fairly vanilla, preferring to stick to what he knows.